1. Field of the Invention
The present invention relates to an image signal coding method and apparatus that generate a sprite image from moving images.
2. Description of the Related Art
In recent years, sprite images have been used as a technique of achieving interactive graphical display on games and the internet. One of conventional techniques of generating a sprite image from moving images is described in JP2000-148130.
According to the description, a sprite image is generated as shown in FIG. 1. First, instep (hereinafter referred to as ST) 1, moving images including portions shot by camera operations such as panning and zooming are input. In ST2, global motion parameters (parameters representing the motion of the entire image) are extracted from the moving images. In ST3, a base frame for generating a sprite is determined in the moving images.
In ST4, predictive images are generated by operating the global motion parameters on frames except the base frame. In ST5 pixel values at sample points are calculated using pixel values in a plurality of other frames. Finally, in ST6, using the pixel values at the sample points calculated in ST6, images of the plurality of other frames each containing a predictive image are arranged for background of the base frame so that images are continuously connected.
However, in the above method, when the foreground has a motion different from the background, it is not possible to accurately estimate global motion parameters between images. As a result such a problem arises that a generated background sprite image is blurred.